Inductance effects on interconnects is an emerging concern in high-performance integrated circuits. Because inductance is related directly to the frequency at which an integrated circuit operates, its effects have traditionally been negligible for circuits operating at relatively low clock speeds. With recent advances in integrated circuit technology, however, higher clock speeds are now attainable at which inductance effects can no longer be ignored.
In general, signal propagation in an integrated circuit can be characterized as operating within two distinct subdomains: the domain where inductance effects are negligible (the rc domain), and the domain where inductance effects are appreciable (the rlc domain). Most wire layouts in an integrated circuit operate in the rc domain where effects from inductance are negligible and where characteristic diffusion times are much longer than the propagation time of electromagnetic waves. Signal propagation on a wire is typically measured in terms of the time needed for the output voltage of a wire to reach one-half of its input value, a value generally accepted as sufficient to produce a transition at a transistor located at the output. This time is referred to as the 50% time delay (t50%). A well-known approximation of the 50% time delay for an open-ended line operating in the rc domain, termed the Sakurai 50% time delay equation, is:t50%=0.377rcL2+0.693RtrcL  (1)where L is the length of the line, r and c are the resistance and capacitance per unit length of the line, respectively, and Rtr is the resistance of the source driving the line. As can be seen from equation (1), the delay exhibits a quadratic increase for longer line lengths L. When delays on rc lines become large, repeaters are often inserted to restore the signal voltage to its maximum driving voltage. Because signal propagation in the rc domain is well-defined and understood, circuit designers and engineers usually attempt to minimize any inductance effects so as not to perturb their traditional design styles. Thus, the natural tendency will be to attempt to minimize inductance so as not to get out of the rlc domain. This approach, however, does not allow signal propagation to occur at its highest possible speed and requires the frequent use of repeaters.